--- title: "River features; hydrological cycle, aquifer" subject: "Engineering Geology I" chapter: 6 key: "semester_3/engineering_geology_i:river-features-hydrological-cycle-aquifer" source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/river-features-hydrological-cycle-aquifer site: BCT Engineering --- # River features; hydrological cycle, aquifer Engineering Geology I · Chapter 6: Physical Geology - Asked in: 2062 Baisakh (old course), 2+6 marks - Video: [Water Cycle | How the Hydrologic Cycle Works](https://www.youtube.com/watch?v=al-do-HGuIk) — National Science Foundation News - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/river-features-hydrological-cycle-aquifer - Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-6 ## Question Describe the various types of morphological features developed by river channels. Define hydrological cycle, permeability, porosity, aquifer and aquiclude. ## Short answer River features include V-valleys, gorges, teraces, meanders, ox-bows, aluvial fans, floodplains, levees, and deltas. Hydrological cycle describes water circulation. Porosity: void ratio (n=V_v/V); permeabilty: fluid transmisson; aquifer yields water; aquiclude stores but doesn't transmit. ## Answer #### Morphological features of river channels **Erosional work** of a river is done by hydraulic action, abrasion, attrition and solution. Features: - **V-shaped valley:** formed by vertical (downward) cutting in the youth stage, in the hills. - **Gorge and canyon:** deep, narrow valley in hard rock, e.g. the Kali Gandaki gorge. - **Waterfall and rapids:** form where hard rock lies over soft rock; a plunge pool forms at the base. - **Potholes:** circular holes drilled in the bed by swirling pebbles. - **River terraces:** step-like old floodplain levels left after the river cuts down again. - **Meanders and ox-bow lakes:** formed by lateral (side) cutting in the old stage. - **Interlocking spurs:** ridges of the valley sides that project alternately into the winding valley of a young river. **Depositional work** occurs when the velocity and carrying capacity fall (on gentle slopes, at the river mouth, and on the floodplain during floods). Features: - **Alluvial fan:** cone-shaped deposit where a mountain stream meets a plain, e.g. the Bhabar zone at the foot of the Siwaliks. - **Floodplain:** broad, flat valley floor built by flood deposits. - **Natural levees:** low ridges of sand and coarse silt built along the banks during floods. - **Braid bars and point bars:** sand and gravel bars in the channel (braid bars) and on the inner bank of bends (point bars). - **Delta:** fan-shaped deposit at the river mouth, e.g. the Ganges-Brahmaputra delta. - **Ox-bow lake and meander scars:** cut-off bends. #### Definitions - **Hydrological cycle:** the continuous circulation of water between the oceans, atmosphere and land: evaporation, condensation, precipitation, runoff, infiltration and groundwater flow back to the sea. - **Porosity ($n$):** ratio of the volume of voids to the total volume of the rock or soil, $n = V_v/V$. It measures the water storage capacity. - **Permeability:** the ability of a material to transmit fluid through its interconnected pores. Gravel is highly permeable; clay is almost impermeable. - **Aquifer:** a saturated rock or soil formation that stores and yields useful amounts of water, e.g. sand, gravel, fractured rock. - **Aquiclude:** a saturated formation that stores water but cannot transmit it in useful amounts, e.g. clay, shale. - **Piezometric level:** the height to which water rises in a well drilled into a confined aquifer; the imaginary surface joining these levels is the piezometric (potentiometric) surface. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. River terraces are: A. Cone-shaped deposits where a stream meets a plain B. Step-like old floodplain levels left after the river cuts down again C. Low ridges of coarse silt along banks D. Fan-shaped deposits at the river mouth Answer: B. When the river incises again, it leaves its old floodplain as steps. (Key point: Terraces) 2. When does a river mainly deposit its load? A. When velocity and slope increase suddenly B. Only in the youth stage in steep hills C. When velocity and load capacity fall, as on gentle slopes, at mouths or in floods D. Only when the water is frozen Answer: C. Reduced velocity means less carrying capacity, so material is dropped. (Key point: Deposition condition) 3. Porosity is defined as: A. The ability to transmit fluid through connected pores B. The ratio of solid volume to void volume C. The height water rises in a confined aquifer D. The ratio of volume of voids to total volume, n = Vv/V Answer: D. Porosity measures storage capacity; permeability measures transmission. (Key point: Porosity) 4. Which pair correctly describes an aquifer and an aquiclude? A. Aquifer stores and yields useful water (sand, gravel); aquiclude stores water but cannot transmit it usefully (clay, shale) B. Aquifer is clay that blocks water; aquiclude is gravel that yields water C. Both yield water, but aquiclude is deeper D. Aquifer is dry rock; aquiclude is saturated sand Answer: A. Both are saturated, but only the aquifer transmits useful amounts. (Key point: Aquifer vs aquiclude) 5. The hydrological cycle is: A. One-way flow of water from land to the ocean only B. Continuous circulation of water between oceans, atmosphere and land C. Formation of rain by wind alone D. Storage of water in aquifers only Answer: B. It includes evaporation, condensation, precipitation, runoff, infiltration and groundwater flow. 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